If you plan to invite your 4 neighbors to see movies, and use it mainly on those occasions, then the addition of a good sub would be appreciated by all.
LFE from movies transmitted by a sub travel through the air and it also creates vibrations that can seriously impact your relationship with close neighbors. You must remember being stopped at a traffic light and hearing the beating of sub from a nearby car...the thing is that you hear the booming sound but not the music. That's what your neighbors will hear.
I live in a bungalow and I remember that a few years ago my next door neighbor's little boy was a mettalic music lover and was using a sub and I could feel the booming through the ground and the foundations separating the two houses (about 25' open space between houses). On one instance, and it was late at night, it was booming so much that I had to go over and ask them to stop.
